The invention relates to a process for the catalytic dimerization of one or more alpha,beta-unsubstituted 1-alkenes having at least three carbon atoms.
Dimerization of alkenes is generally well known in the chemical arts. Under suitable reaction conditions and in the presence of recognized catalysts, one alkene molecule adds to another to form a dimer molecule, which is itself an alkene. Dimerization reactions have commercial utility in the production of chemicals for any number of end uses, for example, in the preparation of high-octane gasoline components or in the synthesis of intermediates in detergent manufacture.
In the preparation of olefin dimers it is most often desirable that the dimerization reaction be selective with regard to formation of dimer product species, and also that formation of polymer by-product in the reaction mixture be minimized. Yet, it is recognized that prior art dimerization procedures are generally characterized by the production of a reaction mixture comprising a substantial amount of higher polymers of the alkene starting material and, in the case of alkenes having three or more carbon atoms, comprising a significant quantity of each of a number of possible dimer product isomers. Thus, for example, when ethylene and/or propylene are dimerized, according to the process of U.S. Pat. No. 3,564,071, in the presence of a complex catalyst consisting of an organo-aluminum compound and an alkyltitanate, the product mixture contains a significant amount of a solid polymer. Furthermore, the reaction of propylene alone according to this patent is shown to have low selectivity to the formation of any of the several possible C.sub.6 dimer species. Likewise, the procedures of Great Britain Patent 896,822 for dimerization of alkenes in the presence of an aluminum dialkyl halide result in a broad range of product dimers and polymers. Similar results are shown in Great Britain Pat. No. 1,058,680 for the reaction of olefins over catalysts comprising certain alkyl metal or allyl metal halide compounds.
Great Britain Pat. No. 840,028 discloses a propylene dimerization process which is shown to be more selective to the production of the single 2-methyl-pentene-1 product when operated in the presence of a catalyst comprising a trialkyl-aluminum and either nickel or platinum. However, the selective results illustrated by this patent are obtained at relatively severe reaction conditions, e.g., a temperature of approximately 250.degree. C. and a pressure of about 120 atmospheres, or, equivalently, about 12,000 kilopascals (kPa). Even more severe conditions, e.g., a temperature exceeding 250.degree. C. and a pressure in the range of 225 to 400 atmospheres, are specified for the dimerization of olefins in the presence of organo-aluminum compounds according to the process of Great Britain Pat. 853,187.